The frequencies of spontaneous abortions, premature births, and birth defects in 121 human pregnancies following relatively infrequent, low doses of medically administered lysergic acid diethylamide are within the normal ranges. The incidence of spontaneous abortions was above average for a small sample of 27 pregnancies where LSD was ingested under both medical and nonmedical conditions. Spontaneous abortions occurred significantly more frequently when the mother received LSD as opposed to the father only; however, the data do not permit the establishment of a clear causal relationship.